<!DOCTYPE HTML>
<html>

<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>nextSibling</title>
</head>

<body>
  <ul id="u1">
    <li id="a">javascript</li>
    <li id="b">jquery</li>
    <li id="c">html</li>
  </ul>
  <ul id="u2">
    <li id="d">css3</li>
    <li id="e">php</li>
    <li id="f">java</li>
  </ul>
  <script type="text/javascript">
    function get_nextSibling(n) {
      let x = n.nextSibling;
      while (x && x.nodeType != 1) {
        x = x.nextSibling;
      }
      return x;
    }

    function get_previousSibling(n) {
      let x = n.previousSibling;
      while (x && x.nodeType != 1) {
        x = x.previousSibling;
      }
      return x;
    }
    var x = document.getElementsByTagName("li")[1];
    document.write(x.nodeName);
    document.write(" = ");
    document.write(x.innerHTML);

    var y = get_nextSibling(x);

    if (y != null) {
      document.write("<br />nextsibling: ");
      document.write(y.nodeName);
      document.write(" = ");
      document.write(y.innerHTML);
    } else {
      document.write("<br>已经是最后一个节点");
    }

    var z = get_previousSibling(x);

    if (z != null) {
      document.write("<br />previousSibing: ");
      document.write(z.nodeName);
      document.write(" = ");
      document.write(z.innerHTML);
    } else {
      document.write("<br>是第一个");
    }
  </script>
</body>

</html>